Coccidiosis of poultry is a disease caused by protozoan parasites of the genus Eimeria. Oocysts of Eimeria species are ubiquitous in the environment and persist for many months in poultry litter. Ingestion of oocysts leads to infection of the various regions of the intestinal tract in a species-specific manner. The organism proliferates in the intestine over a period of several days, resulting in the excretion of the next generation of oocysts in the feces. Multiple cycles of infection lead to immunity, and when the infection is presented to a flock early and in a uniform dosage among the flock, the immunity developed over several cycles of exposure can be quite robust.
In contrast, when birds are not presented with the infection in a uniform manner, situations may arise in which naive birds are subject to sudden, massive infection, leading to poor performance in terms of feed conversion and weight gain, and a high risk of secondary infections. Currently, the most common method used for control of coccidiosis in the poultry industry is not vaccination, but rather the administration of anticoccidial drugs in the feed. The low rate of vaccination is often attributed to uncertainty in the uniformity in dosing via the feed or water at the growout facility or by spray cabinet vaccination at the hatchery, which are the traditional routes and times of administration. There is increasing interest in improving the uniformity of delivery during administration at the hatchery.
Recently, in ovo vaccination techniques have been found applicable to administration of a live oocyst-based coccidiosis vaccine (see, e.g., U.S. Pat. No. 6,500,438; U.S. Pat. No. 6,495,146; and U.S. Pat. No. 6,627,205; all to Pfizer, Inc.). The in ovo route of administration provides a convenient method of delivering a uniform dose of vaccine to each embryo while it is still in the egg. Delivery of avian vaccines in ovo is currently practiced for approximately 85% of the 9 billion broiler birds produced in the United States each year and in a growing percentage of the 21 billion broiler birds produced outside of the United States each year (see, e.g., U.S. Pat. No. 4,458,630; to the United States government). Therefore, the potential market for a live, in ovo-delivered coccidiosis vaccine is considerably larger than the current market for post hatch-delivered coccidiosis vaccines.
Oocysts for use in a live coccidiosis vaccine are derived from feces, which are initially heavily laden with contaminating microorganisms. Typically, regulatory agencies require that in ovo-delivered vaccines be shown to be essentially free of contaminating microorganisms. To ensure that bioburden levels are fully minimized in the final product, it is beneficial to use compositions and methodologies that effectively control the level of contaminating microorganisms at each stage of the oocyst production process. Reduction in extraneous solids may increase the efficiency of bioburden reduction methodologies.
Accordingly, there is a need in the art for improved methods of purifying protozoan oocysts, especially for use in vaccine manufacture.